HETEROCYCLES

■ Contents

■ Terpenoids Bearing the 7-Oxabicyclo[2.2.1]heptane (7-Oxanorbornane) Skeleton. Natural Sources, Biological Activities and Chemical Synthesis

Silvia Roscales and Joaquín Plumet*

*Química Orgánica, Universidad Complutense de Madrid, Ciudad Universitaria, 28040 Madrid, Spain

Abstract

Compounds bearing the 7-oxabicyclo[2.2.1]heptane (7-oxanorbornane) subunits have been used extensively in the synthesis of a large array of complex organic structures. The ease of synthesis of compounds having this substructure in enantiomerically pure form, using Diels-Alder chemistry, is today an almost routinely experimental work. Moreover, the reactivity of these compounds, easily controllable and almost always associated to its ring-strain, makes them particularly valuable chiral building blocks. However, the presence of compounds showing this bicyclic skeleton in Nature has attracted less attention despite its relatively broad distribution. Many of these compounds have been shown to possess important biological activities presenting, in cases, unprecedented biogenetic origin. In addition, some of them have been considered as convenient synthetic targets enabling the development of new synthetic methodologies. In this article we have reviewed different families of terpenoids having in its structure this bicyclic subunit, paying particular attention to their natural sources, biosynthesis, biological activity and chemical synthesis.

■ Redox Responsive Polymer Incorporated with Mesogenic Unit and Bis(benzodithiolyl)bithienyl Scaffold

Toshihiro Ohtake,* Hideki Tanaka, Tetsuro Matsumoto, Mutsumi Kimura, and Akira Ohta*

*Department of Chemistry, Faculty of Science, Shinshu University, Asahi 3-1-1, Matsumoto, Nagano 390-8621, Japan

Abstract

A redox-active polymer consisting of a poly(siloxane) backbone, a liquid crystalline (LC) unit, and bis(benzodithiolyl)bithienyl moieties was designed and synthesized. The resulting polymer after the incorporation of the redox-active and LC functional units into the poly(siloxane) backbone exhibits a redox response associated with the electrochemical interconversion of the bis(benzodithiolyl)bithienyl moieties.

■ An Access to the 13-Membered Cyclophane Substructure in GKK1032As: An Intramolecular 1,4-Addition Approach

Satoka Nagai, Yuka Yamagishi, Yuta Shimizu, Ken-ichi Takao, and Kin-ichi Tadano*

*Department of Applied Chemistry, Emeritus, Keio University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama, Japan

Abstract

The construction of the 13-membered para-cyclophane substructure in GKK1032As, a member of novel pyrrolidinone-containing bioactive natural products, has been explored. An efficient approach for this synthetically formidable object was found, which relied on an intramolecular 1,4-addition between a nitromethylene group and a vinyl ketone moiety both incorporated as side chains into the 6/5/6-tricyclic (the A/B/C-ring system) of the GKK1032s.

■ Removal of Xylylene Groups from Tetrakis(o-xylylenedithio)phthalocyanines with Toluene/Aluminum Chloride and Construction of Dithiaphosphole Rings

Takeshi Kimura* and Shiduko Nakajo

*Center for Instrumental Analysis, Iwate University, 4-3-5 Ueda, Morioka, Iwate 020-8551, Japan

Abstract

Xylylene groups were removed from tetrakis(o-xylylenedithio)phthalocyanines via C-S bond cleavage by treatment with toluene and aluminum chloride. Octathiolate anions generated were reacted with dichlorophenylphosphine to produce phthalocyanines with four dithiaphosphole rings. The structures of the products were determined by NMR and FABMS. Electrochemical and optical properties of them were verified by cyclic voltammetry and UV-vis spectroscopy.

■ Three-Component Coupling Reaction of Enynes, Carbonyls, and Organozinc Reagents

Yuki Ohira, Takamichi Mori, Maya Hayashi, Gen Onodera, and Masanari Kimura*

*Division of Chemistry and Materials Science, Graduate School of Engineering, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

A mixture of t-butylzinc halide and an aldehyde reacts with enyne to provide homopropargyl alcohol in a 1,2-addition manner. Under carbon dioxide at atmospheric pressure, three components (t-butylzinc halide, enyne, and carbon dioxide) combine in a 1:1:1 ratio to give allenyl carboxylic acids in a 1,4-addition manner. These products are useful for the synthesis of heterocyclic compounds such as α,β-unsaturated γ-butyrolactones.

■ Selective Adsorption of Mercury(II) Ion by p-tert-Butylcalix[4]thiacrown-5 at a Solid-Liquid Interface

Tatsuya Takimoto,* Hirohito Tsue, Rui Tamura, and Hideaki Sasaki

*Division of Pharmaceutical Sciences, Faculty of Pharmaceutical Sciences, Kobe Gakuin University, 1-1-3 Minatojima, Chuo-ku, Kobe 650-8586, Japan

Abstract

The solid-liquid adsorption behavior of p-tert-butylcalix[4]thiacrown-5 for heavy metal picrates has been studied. Of four heavy metal ions examined herein, mercury(II) ion was selectively adsorbed, and the saturated adsorption capacity reached to 7.3 ± 0.5 mg g–1.

■ Facile Preparation of 1,2-Dihydroisoquinolines from N-Benzylsulfonamides and Bromoacetylenes

Masahito Yamagishi, Azusa Ishii, Takeshi Hata, and Hirokazu Urabe*

*Department of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan

Abstract

Nucleophilic addition of N-benzylsulfonamides to 1-bromo-1-alkynes proceeded in a highly regio- and stereoselective manner to give (Z)-N-benzyl-N-(1-bromo-1-alken-2-yl)sulfonamides. These adducts cyclized via Pd-catalyzed aromatic C-H bond activation to afford 1,2-dihydroisoquinolines in good yields.

■ Simple, Selective, and Practical Synthesis of 2-Substituted 4(3H)-Quinazolinones by Yb(OTf)3-Catalyzed Condensation of 2-Aminobenzamide with Carboxamides

Tsutomu Yoshimura, Di Yuanjun, Yu Kimura, Hisatsugu Yamada, Akio Toshimitsu, and Teruyuki Kondo*

*Advanced Biomedical Engineering Research Unit, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan

Abstract

A simple, selective, and practical synthetic method of 4(3H)-quinazolinones is realized by Yb(OTf)3-catalyzed condensation of 2-aminobenzamide with carboxamides. As the reaction proceeds, NH3 and H2O were formed as byproducts; however, Yb(OTf)3 can operate as an efficient Lewis acid catalyst without deactivation.

■ Synthesis of Macrocyclic Penta- and Tetraoxazoles as G-Quadruplex Ligands

Shadi Sedghi Masoud, Yamato Tsushima, Keisuke Iida, and Kazuo Nagasawa*

*Biotechnology and Life Science, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16, Naka-cho, Koganei, Tokyo 184-8588, Japan

Abstract

The penta- and tetraoxazole telomestatin analogs L2H2-5OTD (4) and L2H2-4OTD (5) were synthesized as new G-quadruplex ligands in order to evaluate the influence of the size of the planar macrocycle on the G-quadruplex-stabilizing efficacy. These ligands were less potent stabilizers of various G-quadruplex-forming oligonucleotides than L2H2-6OTD (2a), which has a hexaoxazole-type macrocycle.

■ Efficient Preparation of a Versatile Chiral Synthon for 1,2-Diamines via the Fe(III)-Catalyzed Diastereoselective Oxidation of 2-Imidazolone and Its Application

Hirofumi Matsunaga,* Iori Eshita, Shin Ando, and Tadao Ishizuka*

*Department of Pharmaceutical Sciences, Graduate School of Life Sciences, Kumamoto University, 5-1 Oe-hon-machi, Kumamoto 862-0973, Japan

Abstract

The efficient and predominant preparation of (4S,5S)-4,5-dimethoxy-2-imidazolidinone (DMIm) was established via the Fe(III)-catalyzed diastereoselective oxidation of 1-[(1S,2R)-2-exo-alkoxyapocamphanecarbonyl]-2-imidazolone with aqueous H2O2 up to 94% d.e., both of which were easily purified by column chromatography, followed by simple and convenient conversions. The obtained N-tosyl-(4S,5S)-DMIm proved to be a versatile chiral synthon for 1,2-diamines by the synthesis of (1S,2S)-1,2-diamino-1-(4-fluorophenyl)butane derivative, whose platinum complex showed potent antitumor activity.

■ Regioselective Introduction of Substituents to the meso-Position of Pyrromethenone Derivative – Application to the Synthesis of Sterically Fixed Phytochrome Chromophore Anchored to the C15 meso-Position

Yudai Tanaka, Ryoji Iwamoto, Ryo Sakata, Takahiro Soeta, Kohei Endo, Shuhei Fujinami, Katsuhiko Inomata, and Yutaka Ukaji*

*Division of Material Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan

Abstract

Pyrromethenone derivatives corresponding to the CD-ring component of phycocyanobilin chromophore were regioselectively brominated with NBS at the meso-position retaining the stereochemistry of the olefinic carbon skeleton. Subsequent introduction of carbon-substituents to the brominated pyrromethenones was accomplished by treating with Grignard reagents to afford meso-alkylated (E)-isomers regardless of the stereochemistry of the starting brominated pyrromethenones. The resulting product was applied to the synthesis of a meso-anchored sterically fixed tetrapyrrole chromophore.

■ Synthesis of 2,7-Disubstituted 5,10-Diaryl-5,10-dihydrophenazines via Iron-Catalyzed Intramolecular Ring-Closing C–H Amination

Yuma Aoki, Ryuji Imayoshi, Takuji Hatakeyama, Hikaru Takaya, and Masaharu Nakamura*

*International Research Center for Elements Science, Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan

Abstract

A novel iron-catalyzed intramolecular ring-closing C–H amination reaction of o-phenylenediamines was developed, affording the corresponding 2,7-disubstituted 5,10-diaryl-5,10-dihydrophenazines in acceptable yields. The reaction proceeded via the in-situ generation of the magnesium amides of the starting secondary amines in the presence of a catalytic amount of an iron salt and a stoichiometric amount of 1,2-dibromoethane as the terminal oxidant. The substituted dihydrophenazine derivatives can potentially be used as hole-injection materials in organic electroluminescence (OEL) devices and also offer scaffolds for further synthetic elaborations of OEL materials.

■ Synthesis and Structural Analysis of Nine-Membered Enyne Nitrogen Heterocycles

Kazunobu Igawa, Takeshi Kawabata, Kazuhiro Uehara, and Katsuhiko Tomooka*

*Institute for Materials Chemistry and Engineering (IMCE), Kyushu University, 6-1, Kasuga-koen, Kasuga, Fukuoka 816-8580, Japan

Abstract

An efficient approach to the nine-membered enyne nitrogen heterocycle 3 is presented. 1H NMR analysis reveals that both 3a (R = H, X = Ts) and 3b (R = Me, X = Ts) exhibit significant labile planar chirality in solution at ambient temperature. The X-ray analysis of 3b shows that the enantiotopic faces of the alkene are differentiated by the alkyne moiety in the solid state.

■ Theoretical Study on Radical Trifluoromethylation of Silyl Enol Ethers Accelerated via Complexation with Dialkylzinc

Susumu Kawauchi, Yoshihiro Hayashi, Yuichi Tomita, Ryota Hashimoto, Kazuya Honda, Yoshimitsu Itoh, and Koichi Mikami*

*Department of Applied Chemistry, Graduate School of Science and Technology, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan

Abstract

Theoretical study on the electrophilic radical trifluoromethylation of silyl enol ethers is reported to give α-trifluoromethyl carbonyl compounds; the complexation with dialkylzinc accelerates the radical addition of highly electrophilic trifluoromethyl radical to silyl enol ethers via the Zn-π complex (A) rather than the Zn-O complex (B).

■ An Efficient Domino Sonogashira/Double Carbopalladation/C–H-Activation Reaction Leading to Fluorescent Polycyclic Aromatic Hydrocarbons

Lutz F. Tietze* and Christoph Eichhorst

*Institute of Organic and Biomolecular Chemistry, University of Göttingen, Tammannstr. 2, D-37077 Göttingen, Germany

Abstract

A facile synthesis of fluorescent polycyclic aromatic hydrocarbons through a highly productive palladium-catalyzed fourfold domino Sonogashira/double carbopalladation/C–H-activation process was developed.

■ Preparation of (2R,4S)/(2S,4S)-4-Hydroxypipecolinic Acid Derivatives from L-(–)-Malic Acid

Shuqiang Yin, Hiroshi Taneda, Bozhi Li, Dejun Zhou, Daishiro Minato, Kenji Sugimoto, and Yuji Matsuya*

*Graduate School of Medicine and Pharmaceutical Sciences for Research, University of Toyama, Sugitani 2630, Toyama, 930-0194, Japan

Abstract

Synthetically important 4-hydroxypipecolinic acid derivatives were efficiently prepared from commercially available L-(–)-malic acid. The stereochemistries of the derivatives synthesized by our method were determined by coupling constant analyses with key methine protons on C2 and C4.

■ Rhodium-Catalyzed 2-Methylthiolation Reaction of Thiazoles/Oxazoles Using 2-(Methylthio)thiazole

Mieko Arisawa,* Yuri Nihei, and Masahiko Yamaguchi*

*Graduate School of Pharmaceutical Sciences, Tohoku University, Aramaki, Aoba-ku, sendai 980-8578, Japan

Abstract

RhH(PPh3)4 and 1,3-bis(dicyclohexyl)phosphinopropane (dcypp) catalyze the 2-methylthiolation of oxazoles and thiazoles using 2-(methylthio)thiazole as a thiolating reagent. The methylthio transfer reaction is under equilibrium, and various 2-methylthiolated thiazoles and oxazoles were obtained in moderate to good yields by removing thiazole under refluxing o-dichlorobenzene.

■ Enantiodivergent Synthesis of Wieland-Miescher Ketone Analog Mediated by a Chiral Pyridinylmethylamine Derivative

Shota Honda, Kohei Inomata,* and Yasuyuki Endo*

*Faculty of Pharmaceutical Sciences, Tohoku Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai 981-8558, Japan

Abstract

A new enantiodivergent route to provide the Wieland-Miescher ketone analog (3b) bearing a 7-membered ring via the intramolecular aldol reaction of the trione (5) mediated by a single chiral pyridinylmethylamine derivative (13e) was established. Although the enantioselectivities of 3b were moderate, the complete inversion of the enantioselectivities was observed based on the amount of additional trifluoroacetic acid (TFA). The basicity of the nitrogen atom on the pyridine ring was very important for this enantiodivergent behavior.

■ Catalytic and Enantioselective Synthesis of a Key Intermediate of the MCHr1 Antagonist AMG 076

Shinji Harada, Haruka Ishii, Daisuke Shirasaki, and Atsushi Nishida*

*Graduate School of Pharmaceutical Sciences, Chiba University, 1-8-1 Inohana, Chuo-ku, Chiba, Japan

Abstract

A chiral decahydroisoquinoline was constructed using our asymmetric Diels-Alder reaction catalyzed by a chiral Yb (ytterbium) complex as a key step. The decahydroisoquinoline is a synthetic intermediate of the anti-obesity drug candidate AMG 076 (Amgen).

■ Comparison of Photochemical Reactions of Aromatic Carbonyl Compounds with a Silyl Ketene Thioacetal and a Silyl Ketene Acetal

Gyeong Min Moon, Suk Hyun Lim, Dae Won Cho,* Sung Hong Kim, In Ok Lee, Ung Chan Yoon, and Patrick S. Mariano*

*Department of Chemistry and Chemical Biology, University of New Mexico, Albuequerque, NM 87131, U.S.A.

Abstract

Photoaddition reactions of carbonyl compounds with silyl ketene thioacetals have been explored and the results are compared to those arising from investigations of analogus reactions with silyl ketene acetals. Observations made in this study show that photoirradiation of benzaldehyde (8) and benzophenone (9) and with the dimethyl substituted silyl ketene thioacetal (13) promotes reactions that take place predominantly via Paterno-Büchi type [2+2]-cycloaddition pathways to produce oxetanes. In addition, photoreactions between acetophenone (10) and p-cyanoacetophenone (11) and 13 occur via competitive sequential single electron transfer (SET)-desilylation or [2+2]-cycloaddition modes. Lastly, photochemical reaction of the highly electron deficient carbonyl compound, p-trifluoromethylacetophenone (12), and 13 gives rise to exclusive formation of β-hydroxythioester arising via the SET pathway. In contrast, photochemical reactions of all of these aromatic carbonyl compounds with the analogous dimethyl substituted silyl ketene acetal 14 take place predominantly via a sequential SET-desilylation pathway to form β-hydroxyesters. A comparison of these results reveals that replacement of an alkoxy by alkylthio group in the ketene derivatives brings about dramatic changes in chemoselectivities of the photoreactions with aryl-substituted ketones.

■ Macrobicyclic and Macrotricyclic Derivatives of N,N’,N’’,N’’’-Tetrasubstituted Cyclen and Cyclam

Sergei M. Kobelev, Alexei D. Averin, Alexei K. Buryak, Andrei I. Vovk, Valerii P. Kukhar, Franck Denat, Roger Guilard, and Irina P. Beletskaya*

*Department of Chemistry, Lomonosov Moscow State University, Leninskie Gory 1-3, 119991, Moscow, Russia

Abstract

N,N’N’’,N’’’-Tetrabenzyl derivatives of cyclen and cyclam possessing two bromine atoms in trans-positioned phenyl rings were introduced in the Pd-catalyzed amination reactions with oxadiamines and polyamines to provide a wide series of macrobicyclic compounds with tetrabenzyl substituted cyclen and cyclam central moieties in yields up to 31%. Macrocycles based on 1,7-dibenzylcyclen were modified with two 3-bromobenzyl substituents and introduced in the Pd-catalyzed macrocyclization with di- and trioxadiamines to afford spherically shaped macrotricyclic cryptands in yields up to 33%. An alternative approach to isomeric macrotricyclic cryptands employed Pd-catalyzed amination of di(Boc)-di(3-bromobenzyl)cyclen followed by the dialkylation of the resulting bicycle with two bromobenzyl groups and final catalytic macrocyclization step (yields up to 24%).

■ Structural and Ecotoxicological Profile of N-Alkoxymorpholinium-Based Ionic Liquids

Robert Salchner, Gerhard Laus, Simone Haslinger, Volker Kahlenberg, Klaus Wurst, Doris E. Braun, Stefan Vergeiner, Holger Kopacka, Herwig Schottenberger,* Alan Puckowski, Marta Markiewicz, Stefan Stolte, and Sven Nerdinger*

*Faculty of Chemistry and Pharmacy, Leopold-Franzens University, Innrain 80, 6020 Innsbruck, Austria

Abstract

Alkylation of N-methylmorpholine N-oxide (1, NMMO) using dialkyl sulfates gave N-alkyloxymorpholinium alkyl sulfates 2 and 3 (alkyl = Me, Et), which were subjected to ion metathesis. The tetrachloroferrates(III) 4 and 5 were found to be advantageous precursors for the chlorides 6 and 7 which were converted to six other salts. In summary, 13 new quaternary salts were prepared (IO4 8 and 9, BF4 10, N3 11, AcO 12, (MeO)2PO2 13, PF6 14, Tf2N 15) and one hydrate 7·H2O. Eleven X-ray crystal structures were determined. Nine salts had melting points below 100 °C, thus qualifying as ionic liquids (ILs), and three more below 110 °C. In addition, catalytic hydrogenation gave two protic ionic liquids (PILs), N-methylmorpholinium alkyl sulfates 16 and 17 (alkyl = Me, Et). This reductive degradation was also performed in aqueous solution. Ecotoxicological examinations of 3, 4, and 5 showed minor potential to interact with acetylcholinesterase (AChE), moderate acute toxicity towards rat leukemia IPC-81 cells, no adverse effect towards green algae Scenedesmus vacuolatus, but no ready biodegradability in sewage sludge.

■ Simple Synthetic Method for 1-Hydroxyindole and Its Application to 1-Hydroxytryptophan Derivatives

Toshiya Kawasaki, Mutsuko Tabata, Kyoko Nakagawa, Kensuke Kobayashi, Atsushi Kodama, Tetsuya Kobayashi, Masakazu Hasegawa, Keiko Tanii, and Masanori Somei*

*Noto Marine Laboratory, Institute of Nature and Environmental Technology, Faculty of Pharmaceutical Sciences, Graduate School of Natural Science and Technology, Kanazawa University, 56-7 Matsuhidai, Matsudo-shi, Chiba 270-2214, Japan

Abstract

Simple and general synthetic method for 1-hydroxy- and 1-methoxyindole is reported. Its application to the synthesis of various types of 1-hydroxy- and 1-methoxyindole derivatives is successful, especially for the synthesis of 1-hydroxytryptophan derivatives.

■ Facile and Convenient Syntheses for Fluorine-Containing Pyrazolo[4,3-c]quinolines, Isoxazoloquinolines, and 1,4-Diazepino[6,5-c]quinolines

Etsuji Okada,* Mizuki Hatakenaka, and Takushi Sakaemura

*Department of Chemical Science and Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan

Abstract

N,N-Dimethyl-3-trifluoroacetyl-4-quinolylamine underwent an aromatic nucleophilic N-N exchange reaction with hydrazines followed by cyclocondensation to afford the corresponding novel fluorine-containing 1H- and 2H-pyrazolo[4,3-c]quinolines in good to high yields. This reaction could be extended to the synthesis of novel CF3-containing isoxazoloquinolines using hydroxylamine. Furthermore, the use of 1,2-ethylenediamine and 1,2-phenylenediamines gave the corresponding fluorine-containing 1,4-diazepino[6,5-c]quinoline derivatives in high yields.

■ Investigation of Pd(II)-Catalyzed Cyclization of Chiral θ-Hydroxy-α,β,γ,δ-unsaturated Dienol

Akiko Ida, Naoyuki Hoshiya, and Jun'ichi Uenishi*

*Pharmacetuical Chemistry, Kyoto Pharmaceutical University, 1 Shichono-cho, Misasagi, Yamashina-ku, Kyoto 607-8412, Japan

Abstract

PdCl2(MeCN)2 catalyzed intramolecular cyclization of optically pure θ–hydroxyl-α,β,γ,δ−dienylethanols 1 and 2 are described. cis and trans-2- Benzyloxymethyl-6-(1,3-pentadienyl)tetrahydropyrans 3 and 4 were produced stereoselectively with a ratio of 3:1 in excellent yield. No 1,5-chirality transfer was observed in the cyclization reaction.

■ [2+2+2] Cycloaddition of Sulfanylbenzene-Tethered Diynes with Alkynes for the Synthesis of Multi-Substituted Dibenzothiophene Derivatives

Yu-ki Tahara, Riku Matsubara, and Takanori Shibata*

*Chemistry and Biochemistry, Advanced Research Center of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan

Abstract

An intermolecular [2+2+2] cycloaddition of sulfanyl- and sulfonylbenzene-tethered 1,6-diynes with alkynes using rhodium catalysts gave dibenzothiophene derivatives in moderate to excellent yields. The consecutive reaction of tetraynes with an alkyne gave an axially chiral 1,1’-bi(dibenzothiophenyl) and its tetraoxide with up to excellent ee.

■ Synthesis of 1,2-Dialkynyldisilanes Incorporated in 10-Membered-Ring System

Yoshiyuki Mizuhata, Yasunobu Egawa, Takahiro Sasamori, and Norihiro Tokitoh*

*Division of Synthetic Chemistry, Organoelement Chemistry, Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan

Abstract

The reduction of a bis(dichloroethynylsilane) bridged by o-xylylene by lithium naphthalenide afforded trans- and cis-isomers of novel 10-membered-cyclic disilanes. Their structures were characterized by X-ray crystallographic analysis, showing the strain around the C≡C bonds and the close distances between two ethynylene moieties.

■ Chiral Primary Amino Amide Alcohol Organocatalyst for the Asymmetric Michael Addition of 4-Hydroxycoumarin with α,β-Unsaturated Ketones

Jun Kumagai, Yoshihito Kohari, Chigusa Seki, Koji Uwai, Yuko Okuyama, Eunsang Kwon, and Hiroto Nakano*

*Department of Applied Chemistry, Graduate School of Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran, Hokkaido 050-8585, Japan

Abstract

Chiral primary amino amide organocatalysts were designed and synthesized as new organocatalysts for the enantioselective Michael addition of 4-hydroxycoumarin with α,β-unsaturated ketones to produce chiral warfarin (up to 56% ee with up to 92% yield).

■ Oxidative 1,1’-Coupling of Highly Alkylated 2-Methoxycarbonylazulenes

Ryszard Ostaszewski and Hans-Jürgen Hansen*

*Institute of Organic Chemistry, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland

Abstract

The oxidation of highly alkylated methyl azulene-2-carboxylates 1b – 1d and a dimethyl azulene-1,2-dicarboxylate 1a with TEMPO (2,2,6,6-tetramethyl-piperidine-1-oxyl) in the presence of Et2O·BF3 ((diethyloxonio)trifluoroborate) in benzene at 5 °C leads in moderate yield to the corresponding 1,1’-biazulene-carboxylates 2a – 2d (Table 1).